1. Field of Invention
The invention relates to a method for eliminating noise signals and particularly to a method adopted for use in radio signal receiving devices of computer peripherals that are connected to the computer through a universal series bus.
2. Related Art
The Universal Series Bus (USB) is a standard established by USBIF (USB Implement Forum) which is composed of Compaq, Digital, IBM, Intel, Microsoft, NEC, and Nortel in 1995. The current specification is USB v2.0 edition for high-speed transmission bandwidth.
Establishing a USB mainly aims to resolve the chaotic connection interfaces of computer systems and integrates the hardware external interfaces to achieve simple use. Almost all computer peripherals nowadays such as a mouse, keyboard, printer or scanner have adopted a USB as the interface to communicate with the computer.
In order to resolve the messy cabling problem of peripherals such as a mouse or a keyboard, the concept of a TV remote controller in the prior art has been adopted in the functions of a mouse and a keyboard. Take the keyboard for instance; the keyboard may include a radio frequency emission device to correspond to a radio frequency receiving device which is connected to a computer system through a USB interface. When users press a key, the radio frequency emission device transmits a signal package to be received by the receiving device to enable the computer to process a corresponding operation.
However, the data package transmitted by a radio frequency signal tends to be affected or interfered by external environments and the integrity of a data package might suffer. Referring to FIG. 1, the upper portion indicates the complete data bit sets that have been transmitted. The lower portion is the signal after interference has occurred. At present, the function of eliminating or correcting the noise signal bits mostly is accomplished by firmware through a USB chip. Because the cycle of taking samples is too long when a noise signal occurs, it is often not possible to filter the noise signal by the sampling approach. Hence few can pass the certification.
Moreover, take an example, with data bits being 1 and the time length of the data bits being a constant T, the sampling period being T/8, every data bit could include eight sampling bits. If one of the sampling bits is damaged or interfered, the data bit is viewed as ineffective. And the entire data package is treated as an error. As a result, users have to operate again and send a series of data anew. This causes huge inconvenience.